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Executive Summary Background The International Cooperative Programme on Effects of Air Pollution on Natural Vegetation and Crops (ICP Vegetation) was established in the late 1980s. It is led by the UK and has its Programme Coordination Centre at the Centre for Ecology and Hydrology (CEH) in Bangor. It is one of seven ICPs and Task Forces that report to the Working Group on Effects (WGE) of the Convention on Longrange Transboundary Air Pollution (LRTAP Convention) on the effects of atmospheric pollutants on different components of the environment (e.g. forests, fresh waters, materials) and health in Europe and North-America. Today, the ICP Vegetation comprises an enthusiastic group of over 200 scientists from 35 countries in the UNECE region with outreach activities to other regions such as Asia, Central America and Africa. An overview of contributions to the WGE workplan and other research activities in the year 2010/11 is provided in this report.

Annual Task Force Meeting

The Programme Coordination Centre organised the 24th ICP Vegetation Task Force Meeting, 31 January - 2 February 2011 in Rapperswil-Jona, Switzerland, in collaboration with the local hosts at FUB (Forschungsstelle für Umweltbeobachtung) – Research Group for Environmental Monitoring. The meeting was attended by 68 experts from 26 countries, including a representative from EMEP/MSC-East and guests from Egypt, India, Pakistan and South Africa. The Task Force discussed the progress with the workplan items for 2011 and the medium-term workplan for 2012 - 2014 for the air pollutants ozone, heavy metals, nutrient nitrogen and persistent organic pollutants (POPs). For ozone, four expert groups were established to support the future work programme.

Reporting to the Convention and other publications In addition to this report, the ICP Vegetation Programme Coordination Centre has provided technical reports on ‘Effects of air pollution on natural vegetation and crops’ and contributed to the joint report and two other reports of the WGE. It also published a glossy report and summary brochure for policy makers on the threat of ozone to food security. Further analyses on the relationship between heavy metal concentrations in mosses and modelled atmospheric depositions were reported in the EMEP Status Report 2/2011. Eight scientific papers have been published or are currently in press. The ICP Vegetation web site was updated regularly with new information.

Contributions to the WGE common workplan Further implementation of Guidelines on Reporting of Monitoring and Modelling of Air Pollution Effects The ICP Vegetation continued to monitor and model deposition to and impacts on vegetation for the air pollutants ozone, heavy metals, nitrogen and POPs. In addition, it conducted a review on the impacts of black carbon on vegetation. Comparison of activities across continents and regions (North America, Western Europe, and SouthEastern Europe (SEE), Eastern Europe, the Caucasus and Central Asia (EECCA)) Recently, the ICP Vegetation has been most active in Western Europe, followed by SEE and participation from three EECCA countries. Outreach activities have risen in recent years and have taken place with Asia (China, India, Japan, Pakistan), Cuba, Egypt and South Africa. Ex-post analysis To support the revision of the Gothenburg Protocol, the WGE has conducted an analysis on the impacts of air pollution on ecosystems, human health and materials under different emission scenarios, including the application of recently developed effects indicators such as the phytotoxic ozone dose (POD; flux-based approach). Results show that despite predicted reductions in both ozone concentrations and stomatal fluxes in 2020, large areas in Europe will remain at risk from adverse impacts of ozone on vegetation, even after implemation of maximum technically feasible reductions, with areas at highest risk being predicted in parts of central and southern Europe.

Progress with ICP Vegetation-specific workplan items in 2010/11 The 2010 biomonitoring exercise for ozone Since 2008, participants of the ICP Vegetation have been conducting biomonitoring campaigns using ozone-sensitive (S156) and ozone-resistant (R123) genotypes of Phaseolus vulgaris (Bush bean, French Dwarf bean). In 2010, there was a good linear relationship between the S/R pod number and pod weight ratio, with a decline in ratio with increasing ozone concentration. A stomatal flux model was developed and parameterised for bean using data collated so far. At the 24th Task Force meeting is was decided to scale down ozone biomonitoring experiments in the future. Ozone impacts on food security The ICP Vegetation reviewed the threat of ozone to food security (Mills et al., 2011a). Current ambient ozone concentrations are affecting both crop yield and quality. Mean losses for various crops are estimated to be in the range of 10 – 20%, both in Europe and South Asia. Applying the flux-based methodology for wheat and tomato, mean yield losses were predicted to be 13.7 and 9.4% in 2000 in EU27+Norway+Switzerland, amounting to an economic loss of 3.20 and 1.02 billion Euros for wheat and tomato respectively. Implementation of current legislation (NAT2020 scenario) is predicted to result in a decline in yield loss to 9.1 and 5.7% and economic losses to 1.96 and 0.63 billion Euros for wheat and tomato respectively in 2020. However, widespread exceedance of ozone critical levels for wheat and tomato yield will remain in 2020 with exceedance occurring in 82 and 51% of EMEP grid squares (where the crops are grown) respectively. Impacts of black carbon on vegetation Little is known about the direct impacts of black carbon on vegetation. Black carbon generally increases leaf temperature which will affect plant growth and physiology. (Road) dust in general might block stomata, affecting stomatal function. Increases in leaf temperature, transpiration and uptake of gaseous pollutants have been reported, together with decreases in photosynthesis due to shading or impeded diffusion after exposure to dust. Indirect effects of black carbon on vegetation include atmospheric warming and a change in direct-to-diffuse radiation ratio, affecting plant photosynthesis. Progress with European heavy metals and nitrogen in mosses survey 2010/11 Between 24 – 27 countries will submit data on heavy metals, of which 14 countries will also submit data on nitrogen concentrations in mosses. In addition, six countries will submit data on POPs, polycyclic aromatic hydrocarbons (PAHs) in particular. Mosses as biomonitors of POPs A review of the literature has shown that mosses can potentially be used as biomonitors of POPs. However, mosses have often been applied to indicate POPs pollution levels in remote areas or to determine gradients near pollution source, only few studies have attempted to relate POPs concentrations in mosses with atmospheric concentrations and/or deposition fluxes. Many studies have focussed on PAHs, more studies are needed on other POPs, in particular those recently targeted in air pollution abatement policies.

New activities of the ICP Vegetation The ICP Vegetation Task Force has agreed to conduct the following reviews, and publish a glossy report and summary brochure for policy makers, on:  Impacts of ozone on carbon sequestration and ozone absorption by vegetation and the implications for climate change (2012);  Ozone impacts on biodiversity and ecosystem services (2013). In addition, it will review the relationship between i) heavy metal and ii) nitrogen concentrations in mosses and impacts on ecosystems (2012).

1 Introduction 1.1 Background The International Cooperative Programme on Effects of Air Pollution on Natural Vegetation and Crops (ICP Vegetation) was established in the late 1980s, initially with the aim to assess the impacts of air pollutants on crops, but in later years also on (semi-)natural vegetation. The ICP Vegetation is led by the UK and has its Programme Coordination Centre at the Centre for Ecology and Hydrology (CEH) in Bangor. The ICP Vegetation is one of seven ICPs and Task Forces that report to the Working Group on Effects (WGE) of the Convention on Long-range Transboundary Air Pollution (LRTAP Convention) on the effects of atmospheric pollutants on different components of the environment (e.g. forests, fresh waters, materials) and health in Europe and North-America. The Convention provides the essential framework for controlling and reducing damage to human health and the environment caused by transboundary air pollution. So far, eight international Protocols have been drafted by the Convention to deal with major long-range air pollution problems. ICP Vegetation focuses on the following air pollution problems: quantifying the risks to vegetation posed by ozone pollution and the atmospheric deposition of heavy metals, nitrogen and persistent organic pollutants (POPs) to vegetation. Currently, the work of the ICP Vegetation contributes to the revision of the Gothenburg Protocol (scheduled to be finaliased by the end of 2011), aiming to abate acidification, eutrophication and ground-level ozone. Today, the ICP Vegetation comprises an enthusiastic group of over 200 scientists from 35 countries in the UNECE region (Table 1.1). In addition, scientists from China, Cuba, Egypt, India, Japan, Pakistan and South Africa participate as the ICP Vegetation stimulates outreach activities to other regions in the world and invites scientists in those regions to collaborate with and participate in the programme of the ICP Vegetation. The contact details for lead scientists for each group are included in Annex 1. In many countries, several other scientists (too numerous to mention individually) also contribute to the biomonitoring programmes, analysis and modelling procedures of the ICP Vegetation. Table 1.1. Countries participating in the ICP Vegetation; in italics: not a Party to the LRTAP Convention. Albania Austria Belarus Belgium Bulgaria China Croatia Cuba Czech Republic Denmark Egypt Estonia Finland France

released due to anthropogenic emissions (especially from vehicle sources) increase the concentration of ozone in the troposphere. These emissions have caused a steady rise in the background ozone concentrations in Europe and the USA since the 1950s (The Royal Society, 2008). Superimposed on the background tropospheric ozone are ozone episodes where elevated ozone concentrations in excess of 50-60 ppb can last for several days. Ozone episodes can cause short-term responses in plants such as the development of visible leaf injury (fine bronze or pale yellow specks on the upper surface of leaves) or reductions in photosynthesis. If episodes are frequent, longer-term responses such as reductions in growth and yield and early die-back can occur. The negotiations concerning ozone for the Gothenburg Protocol (1999) were based on exceedance of a concentration-based critical level of ozone for crops and (semi-)natural vegetation. This value, an AOT40 of 3 ppm h accumulated over three months was set at the Kuopio Workshop in 1996 (Kärenlampi and Skärby, 1996) and is still considered to be the lowest AOT40 at which significant yield loss due to ozone can be detected for agricultural crops and (semi-)natural vegetation dominated by annuals, according to current knowledge (LRTAP Convention, 2010). However, several important limitations and uncertainties have been recognised for using the concentration-based approach. The real impacts of ozone depend on the amount of ozone reaching the sites of damage within the leaf, whereas AOTX-based critical levels only consider the ozone concentration at the top of the canopy. The Gerzensee Workshop in 1999 (Fuhrer and Achermann, 1999) recognised the importance of developing an alternative critical level approach based on the flux of ozone from the exterior of the leaf through the stomatal pores to the sites of damage (stomatal flux). This flux-based method provides an indication of the degree of risk for adverse effects of ozone on vegetation with a stronger biological basis than the concentration-based method. The flux-based approach required the development of mathematical models to estimate stomatal flux, primarily from knowledge of stomatal responses to environmental factors (Emberson et al., 2000; Pleijel et al., 2007). During 2009/10, flux-based critical levels of ozone for vegetation were reviewed at an LRTAP Convention workshop in Ispra, November 2009 and new/revised flux-based critical levels were agreed at follow-on discussions at the 23rd ICP Vegetation Task Force meeting, February 2010 (Harmens et al., 2010; LRTAP Convention, 2010; Mills et al., 2011c). They include policy-relevant indicators for i) agricultural crops to protect security of food supplies; ii) forest trees to protect against loss of carbon storage in living trees and loss of other ecosystem services such as soil erosion, avalanche protection and flood prevention; iii) grassland (productive grasslands and grassland of high conservation value) to protect against for example loss of vitality and fodder quality. The Executive Body of the LRTAP Convention decided at its 25th meeting in December 2007 (ECE/EB.AIR/91) to start the revision of the Gothenburg Protocol by mandating the Working Group on Strategies and Review to commence, in 2008, negotiations on further obligations to reduce emissions of air pollutants contributing to acidification, eutrophication and ground-level ozone. The outcome of the revision is currently scheduled to be presented to the Executive Body in December 2011. The ozone sub-group of the ICP Vegetation contributes models, state of knowledge reports and information to the LRTAP Convention on the impacts of ambient ozone on vegetation; dose-response relationships for species and vegetation types; ozone fluxes, vegetation characteristics and stomatal conductance; flux modelling methods and the derivation of critical levels and risk assessment for policy application.

1.2.2

Heavy metals

Concern over the accumulation of heavy metals in ecosystems, and their impacts on the environment and human health, increased during the 1980s and 1990s. Currently some of the most significant sources include:     

The heavy metals cadmium, lead and mercury were targeted in the 1998 Aarhus Protocol as the environment and human health were expected to be most at risk from adverse effects of these metals. Atmospheric deposition of metals has a direct effect on the contamination of crops used for animal and human consumption (Harmens et al., 2005). The ICP Vegetation is addressing a short-fall of data on heavy metal deposition to vegetation by coordinating a well-established programme that monitors the deposition of heavy metals to mosses. The programme, originally established in 1980 as a Swedish initiative, involves the collection of naturally-occurring mosses and determination of their heavy metal concentration at five-year intervals. Surveys have taken place every five years since 1980, with the four most recent surveys being panEuropean in scale. Ca. 6,000 moss samples have been collected in 28 countries in the 2005/6 European survey. Spatial and temporal trends (1990 – 2005) in the concentrations of heavy metals in mosses across Europe have been described by Harmens et al. (2008; 2010). Detailed statistical analysis showed that spatial variation in the cadmium and lead concentrations in mosses is primarily determined by the atmospheric deposition of these metals, whereas it’s less clear which factor primarily determines the mercury concentration in mosses (Holy et al., 2010; Schröder et al., 2010b). Currently data are collated for the 2010/11 European moss survey, including data on nitrogen and a pilot study on POPs (see sections 3.2.4 and 3.2.5).

1.2.3

Nitrogen

In recent decades, concern over the impact of nitrogen on low nutrient ecosystems such as heathlands, moorlands, blanket bogs and (semi-)natural grassland has increased. The empirical critical loads for nitrogen were reviewed and revised recently (Bobbink and Hettelingh, 2011; ECE/EB.AIR/WG.1/2010/14). In 2009, the WGE gathered evidence on the impacts of airborne nitrogen on the environment and human health with the aim of drawing attention to the current threat of atmospheric nitrogen deposition to the environment and human health (ECE/EB.AIR/WG.1/2009/15). Details on the contribution of the ICP Vegetation can be found in Harmens et al. (2009). Previously, plant communities most likely to be at risk from both enhanced nitrogen and ozone pollution across Europe were identified (Harmens et al., 2006). In 2005/6, the total nitrogen concentration in mosses was determined for the first time at almost 3,000 sites to assess the application of mosses as biomonitors of nitrogen deposition at the European scale (Harmens et al., in press; Schröder et al., 2010a). The European nitrogen in moss survey is currently being repeated for 2010/11. There are many groups within Europe studying atmospheric nitrogen fluxes and their impact on vegetation (e.g. Nitrogen in Europe (NinE), NitroEurope, COST 729). The ICP Vegetation maintains close links with these groups to provide up-to-date information on the impacts of nitrogen on vegetation to the WGE of the LRTAP Convention. Recently, the report of the European Nitrogen Assessment (ENA) was published (http://www.nine-esf.org/ENA-Book).

1.2.4

Persistent organic pollutants (POPs)

POPs are organic substances that possess toxic and/or carcinogenic characteristics, are degrading very slowly, bioaccumulate in the food chain and are prone to long-range transboundary atmospheric transport and deposition. In 1998, the Aarhus Protocol on POPs was adopted and a list of 16 substances was targeted to eliminate any discharges, emissions and losses in the long term. In 2009, seven new substances were included. In 2001, the Stockholm Convention on POPs was established as a global treaty under the United Nations Environment Programme (UNEP), and new substances were added in 2009. Mosses are known to accumulate POPs (see section 3.2.5) and in the currently ongoing European moss survey of 2010/11 some countries will determine the concentration of selected POPs (polycyclic aromatic hydrocarbons (PAHs) in particular) in mosses in a pilot study to investigate the suitability of mosses as biomonitors of POPs at a regional scale (see section 3.2.4).

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1.3 Workplan items for the ICP Vegetation in 2011 The following activities were agreed at the 28th session of the Executive Body of the LRTAP Convention (ECE/EB.AIR/106/Add.2) to be priority areas of work for the ICP Vegetation in 2011: 

Report on the 2010 biomonitoring exercise for ozone;



Report on ozone impacts on food security;



Report on effects of black carbon deposition on vegetation;



Progress report on European heavy metals and nitrogen in mosses survey 2010/11;



Report on mosses as biomonitors of POPs;

In addition, the ICP Vegetation was requested to report on the following common workplan items of the WGE: 

Report on the further implementation of the Guidelines on Reporting of Monitoring and Modelling of Air Pollution Effects;



Report on the heavy metals baseline assessment;



Reports on the comparison of activities across continents and regions (North America, Western Europe, and South-Eastern Europe, Eastern Europe, the Caucasus and Central Asia);



Report on ex-post analysis.

Progress with each of these workplan activities is described in Chapter 3, with details of the ozone impacts on food security being described in Chapter 4. New activities of the ICP Vegetation are described in Chapter 5 and Chapter 6 summarises the key achievements in 2010/11 together with the medium-term workplan for 2012 – 2014 (up-dated at the 24th ICP Vegetation Task Force Meeting, 31 January – 2 February 2011, Rapperswil-Jona, Switzerland).

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2 Coordination activities 2.1 Annual Task Force Meeting The Programme Coordination Centre organised the 24th ICP Vegetation Task Force meeting, 31 January – 2 February 2011 in Rapperswil-Jona, Switzerland, in collaboration with the local hosts at FUB (Forschungsstelle für Umweltbeobachtung) – Research Group for Environmental Monitoring. The meeting was attended by 68 experts from 26 countries, including 22 Parties to the LTRAP Convention, a representative from EMEP/MSC-East and four guests from Egypt, India, Pakistan and South Africa. The Task Force discussed the progress with the workplan items for 2011 (see Section 1.3) and the medium-term workplan for 2012 - 2014 (see Section 6.2) for the air pollutants ozone, heavy metals, nutrient nitrogen and POPs. A book of abstracts, details of presentations and the minutes of the 24th Task Force meeting are available from the ICP Vegetation web site (http://icpvegetation.ceh.ac.uk). The main decisions made at the Task Force meeting were: Ozone and black carbon – i) To scale down ozone biomonitoring activities; (ii) To produce state of knowledge reports on the impacts of ozone on: - Carbon sequestration and linkages with climate change (2012); - Biodiversity and ecosystem services (2013); - Vegetation in a changing climate (tentatively; 2014). iii) To conduct an initial review on the impacts of black carbon on vegetation (see Section 3.2.3). In addition, ozone expert groups on the following themes were established to support current and future work on the impacts of ozone on vegetation: - Ozone and climate change interactions (including interactions with nitrogen); - Ongoing flux model development, and concentration and flux map validation; - Ozone impacts on carbon sequestration; - Outreach activities. Heavy metals, nitrogen and POPs – To continue with the moss biomonitoring activities on heavy metals, nitrogen and POPs, and encourage expansion in countries from Southern-Eastern Europe (SEE), Eastern Europe, Caucasus and Central Asia (EECCA) and outreach to other parts of Asia. In addition, the representative of EMEP/MSC-East reiterated how useful the moss data on heavy metals were for assessing the performance of the regional model MSCE-HM of heavy metal transboundary air pollution in Europe at a higher spatial resolution. The Task Force acknowledged and encouraged further fruitful collaborations with the bodies and centres under the Steering Body to EMEP, in particular EMEP/MSC-West, EMEP/MSC-East, the Task Force on Integrated Assessment Modelling and the Task Force on the Hemispheric Transport of Air Pollution, and bodies under the Working Group of Strategies and Review, in particular the Task Force on Reactive Nitrogen. In addition, the Task Force encouraged further development of outreach activities to other regions in the world. The 25th Task Force meeting will be hosted by the University of Brescia, Italy, from 30 January – 1 February 2012.

2.2 Reports to the LRTAP Convention The ICP Vegetation Programme Coordination Centre has reported progress with the 2011 workplan session of the WGE items in the following documents for the 30th (http://www.unece.org/env/lrtap/WorkingGroups/wge/30meeting.htm): - ECE/EB.AIR/WG.1/2011/3: Joint report of the ICPs and Task Force on Health;

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- ECE/EB.AIR/WG.1/2011/8: Effects of air pollution on natural vegetation and crops (technical report from the ICP Vegetation); For the draft workplan for 2012 - 2013, see ECE/EB.AIR/GE.1/2011/10. In addition, the Programme Coordination Centre for the ICP Vegetation has: - published a glossy report on ‘Ozone pollution: A hidden threat to food security’ (Mills et al., 2011a) and a colour summary brochure for policy makers (see Chapter 4); - published the current annual glossy report; - contributed to a colour brochure of the WGE on ‘30 years of effects research under the Convention of Long-range Transboundary Air Pollution’ - provided text for an interim report on the ex-post analysis of the WGE to support the revision of the Gothenburg Protocol (see Section 3.1.4). Further analyses on the relationship between heavy metal concentrations in mosses and modelled atmospheric depositions were reported in the EMEP Status Report 2/2011.

3 Ongoing research activities in 2010/11 In this chapter, progress made with the WGE common workplan items and the ICP Vegetation workplan for 2011 is summarised.

3.1 Contributions to WGE common workplan items 3.1.1

Report on the further implementation of the Guidelines on Reporting of Air Pollution Effects

Table 3.1 provides an overview of the monitoring and modelling effects reported by the ICP Vegetation according to the Guidelines (ECE/EB.AIR/2008/11). Table 3.1. Monitoring and modelling effects reported by the ICP Vegetation. Parameter

At the Extended Bureau meeting of the WGE (15 – 16 February 2011, Geneva) it was agreed that the ICP Modelling and Mapping would report on this issue on behalf of all ICPs. Hence, we refer to the 2011 status report of the Coordination Centre for Effects and ECE/EB.AIR/WG.1/2011/10 for further details.

3.1.3

Reports on the comparison of activities across continents and regions

Table 3.2 provides a comparison of the recent participation of countries from different continents and regions in activities of the ICP Vegetation. The ICP Vegetation was most active in Western Europe, followed by South-Eastern Europe (SEE) and some countries in Eastern Europe, the Caucasus and Central Asia (EECCA). Some outreach activities took place recently with Asia (China, India, Japan, Pakistan), Cuba, Egypt and South Africa. Table 3.2. Number of countries from different continents and regions participating recently in activities of the ICP Vegetation. Activity Ozone-related activities Moss survey Task Force meeting 2011

Western Europe

SEE

EECCA

North America

Other regions

Total

11 19 13

3 9 6

1 3 3

1 -

7 1 4

23 32 26

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3.1.4

Report on ex-post analysis by the Working Group on Effects

Background To support the revision of the Gothenburg Protocol, the WGE has conducted an analysis on the impacts of air pollution on ecosystems, human health and materials under different emission scenarios. The objectives of this analysis are to:  



Provide information on effects of air pollution on ecosystems, human health and materials to support decisions for the revision of the Gothenburg Protocol; Demonstrate application of new science and effects indicators, developed since 1999 and currently not included in the GAINS (Greenhouse Gas and Air Pollution Interactions and Synergies) model, to illustrate the potential impact of policy/decisions on the environment, human health and materials; Illustrate effectiveness of emission scenarios to improve the environment and human health.

This analysis has been carried out by the International Cooperative Programmes (ICPs) and Task Force on Health under the WGE between October 2010 and February 2011. The analysis is based on scenarios of air pollutant emissions provided by the Task Force on Integrated Assessment Modelling (TFIAM), the Centre on Integrated Assessment Modelling (CIAM) and the European Monitoring and Evaluation Programme (EMEP) in October 2010 (described in CIAM report 1/2010). The scenarios included in the report are (CIAM report1/2010):  NAT2000: historical data for the year 2000 based mainly on national information;  NAT2020: data generated under a current legislation scenario for 2020 based mainly on national information about future economic projections;  PRI2020 and PRI2030: data generated under a current legislation scenario for 2020 and 2030 and based mainly on economic projections developed by the PRIMES model;  MTFR2020: data based on a scenario assuming all technically feasible technologies being implemented by 2020. NAT and PRI projections are considered to represent “baseline” scenarios: they provide the emissions as they are expected to occur if no new regulations are implemented. MTFR represents emission reduction that would be expected if the most stringent regulations were implemented using current available technology. Any decision leading to some emission reduction will lead to a situation between the baseline and the MTFR scenario. Further details on these projections and scenarios are specified in CIAM report 1/2010. Emissions scenarios have undergone some revisions since October 2010, mainly to respond to requests from the Working Group on Strategy and Review (WGSR). It is therefore expected that an update of the analysis will be carried out in the summer/autumn 2011 to ensure compatability with emission scenarios that will be used in the final stage of the Gothenburg Protocol revision (scheduled for the end of 2011). Crop yield and economic losses based on new ozone effects indicators For the development of the 1999 Gothenburg Protocol, AOT402 was used to indicate the risk to vegetation of adverse impacts of ozone. Since then, a biologicially more relevant impact indicator has been developed, the Phytotoxic Ozone Dose above a threshold Y (PODY), which gives a better correlation between the locations where ozone damage was reported in Europe between 1990 and 2006 and maps of ozone flux (PODY) than maps of AOT40 (Hayes et al., 2007b; Mills et al., 2011b). Recently, new or revised flux-based critical levels were developed for crops (potato, tomato, wheat), trees (beech/birch, Norway spruce) and white clover as a representative species of grasslands and (semi-)natural vegetation (Harmens et al., 2010; LRTAP Convention, 2010; Mills et al., 2011c).

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The sum of the differences between the hourly mean ozone concentration (in ppb) and 40 ppb for each hour when the concentration exceeds 40 ppb, accumulated during daylight hours. 8

Using the flux-based approach and NAT scenarios, economic losses due to ozone for wheat were estimated to be 3.2 billion euros in EU27+Switzerland+Norway in 2000 reducing to 1.96 billion euros in 2020 (Table 3.3). Although the percentage wheat yield reduction is predicted to decline in 2020, only a very small reduction in the proportion of EMEP grid squares exceeding the critical level is predicted. Proportional reductions in yield and economic value for tomato, an important crop for southern areas, were similar to those for wheat for NAT2020 compared to NAT2000 (Table 3.3). Table 3.3. Predicted impacts of ozone pollution on wheat and tomato yield and economic value, together with critical level exceedance in EU27+Switzerland+Norway in 2000 and 2020 under the current legislation scenario (NAT scenario). Analysis was conducted on a 50 x 50 km EMEP grid square using crop values in 2000 and an ozone stomatal flux-based risk assessment. Crop Emission scenario

Wheat

Tomato

NAT2000

NAT2020

NAT2000

NAT2020

Economic losses (billion Euro)

3.20

1.96

1.02

0.63

Percentage of EMEP grid squares exceeding critical level*

84.8

82.2

77.8

51.3

Mean yield loss (%)*

13.7

9.1

9.4

5.7

* Calculated for the grid squares where the crop is grown. See table 4.3 for details per country. Mapping different ozone effect indicators Here we compare the ozone flux-based risk maps for a generic deciduous tree (LRTAP Convention, 2010) with the ozone concentration-based risk maps for forest trees (AOT40) and human health (SOMO353). Concentration-based maps using AOT40 or SOMO35 predict that southern European areas are most at risk from adverse impacts of ozone (Figure 3.1). However, the ozone flux-based map indicates that in addition, large areas of central and northern Europe are also at considerable risk (Figure 3.1). This effect is even more pronounced when applying the MTFR2020 and the PRIMES2030 scenarios (Figure 3.2). The effect can be explained by the favourable climatic conditions (e.g. high humidity) that enhance ozone stomatal flux in northern (and central) Europe at moderate ozone concentrations, whilst lower humidity and higher temperature in southern Europe tend to reduce stomatal ozone flux at relatively high ozone concentrations. This not only confirms previous results showing that policies aiming only at health effects would not protect vegetation in large areas of Europe (ECE/EB.AIR/96; Mills et al., 2008), but also indicates that the additional risk to vegetation in the northern third of Europe is of even more concern for future emission scenarios. Comparison of ozone risk maps for vegetation applying the different projections shows that despite the predicted reductions in both ozone concentrations and stomatal fluxes in the future, large areas in Europe will remain at risk from adverse impacts of ozone on vegetation, with areas at highest risk being predicted in parts of central and southern Europe. Although in the future the severity of risk of adverse impacts of ozone on tree biomass is expected to decline, the total area of considerable impact is hardly reduced (Figure 3.1 and 3.2; conform table 3.3). Even under the MTFR scenario for 2020, large areas in Europe are at risk from adverse impacts of ozone on vegetation. The same is true for human health (data not shown).

3

Yearly sum of the daily maximum 8h means that exceed 35 ppb ozone 9

AOT40 (forest)

SOMO35 (human health)

POD1 (generic tree)

Figure 3.1. The risk of adverse ozone impacts on biomass production in forest based on AOT40 (the AOT40-based critical level is 5 ppm.h) and on the generic deciduous tree flux model (POD1) in comparison with the risk of adverse ozone impacts on human health (SOMO35). The maps were produced using the NAT2000 projection and colour classes have been scaled in the same way for each metric based on the highest values to allow direct comparison. NAT2020

MTFR2020

PRI2030

Figure 3.2. The risk of adverse ozone impacts on biomass production in forest using the generic deciduous tree flux model (POD1) for NAT2020, MTFR2020 and PRI2030. Colour classes have been scaled in the same way for each metric based on the highest values to allow direct comparison.

3.2 Progress with ICP Vegetation workplan items 3.2.1

The 2010 biomonitoring exercise for ozone

Background Since 2008, participants of the ICP Vegetation have been conducting biomonitoring campaigns using ozone-sensitive (S156) and ozone-resistant (R123) genotypes of Phaseolus vulgaris (Bush bean, French Dwarf bean) that had been selected at the USDA-ARS Plant Science Unit field site near Raleigh, North Carolina, USA. The bean lines were developed from a genetic cross reported by Dick Reinert (described in Reinert and Eason (2000)). Individual sensitive (S) and tolerant (R) lines were identified, the S156 and R123 lines were selected, and then tested in a bioindicator experiment reported in Burkey et al. (2005). A trial of this system occurred in central and southern parts of Europe during the summer of 2008. This was extended in 2009 and included again in the ozone biomonitoring programme for 2010. For ICP Vegetation biomonitoring studies in 2010, bean seeds of the strains S156 and R123 were kindly provided by Kent Burkey (USA). Bean seeds and an experimental protocol (ICP Vegetation, 2010) were supplied by the Programme Coordination Centre to participants across Europe. Beans were supplied to 17 sites from 10 countries in April 2010. Exposure to ambient air began in May-June

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at the majority of sites, with participants continuing the experiment until six weeks after the onset of flowering (typically at the end of August). In addition to records of visible injury and pod yield at almost all sites, stomatal conductance measurements were made in UK-Ascot, Spain-Valencia, Italy-Rome, Greece-Kalamata and Greece-Crete. These were combined with measurements made in 2008 and 2009 to give a database of over 3000 stomatal conductance data in ambient air. Plant, climate and pollutant data were received by the Programme Coordination Centre from 12 sites in eight countries in 2010 (Table 3.4) In addition to the ambient air experiment, exposure studies were also carried out in chambers in UK-Bangor, UK-Ascot, Italy-Curno and Germany-Giessen. Ozone conditions A summary of the ozone concentration data received is shown in Table 3.4. The AOT40 during the exposure period ranged from 0.4 ppm.h (UK-Bangor) to 7.0 ppm.h (Greece-Kalamata) across Europe, with an AOT40 of 10.2 ppm.h being reported in Japan-Criepi. The 12-h mean ozone concentration during the exposure period ranged from 24.0 ppb (UK-Ascot) to 48.5 ppb (Spain-Valencia) in Europe and was 46.7 ppb in Japan-Criepi. Table 3.4. Ozone concentration (12-h mean) and AOT40 at ICP Vegetation sites during exposure of R123 and S156 bean plants to ambient air in 2010. Site Austria-Seibersdorf Belgium-Tervuren Greece-Crete Greece-Kalamata Italy-Pisa Italy-Rome Japan-Criepi (site 1) Japan-Criepi (site 2) Spain-Valencia UK-Ascot UK-Bangor Ukraine-Kiev

Visible injury More extensive and severe injury was reported on the ozone sensitive variety. However, approximately half of all sites also recorded visible injury on the resistant variety. For most sites progression of visible leaf injury was fairly constant throughout the exposure period. There was no clear relationship between visible injury and either 12-h mean ozone concentration or AOT40 (data not shown). Yield Generally there was a good relationship between S156/R123 pod number and pod weight ratio, with a decline in ratio with increasing ozone concentration (Figure 3.3a,b). The relationship was better for pod weight (excluding one outlier, r2=0.85) than for pod number (r2=0.62). There were fewer data points for seed number and seed weight, however, the S156/R123 seed number ratio also showed a decrease with increasing ozone concentration (Figure 3.3c). Stomatal flux model development Boundary line analysis of the bean stomatal conductance data was carried out to parameterise a stomatal flux model for bean based on the response of stomatal conductance to light, temperature and preliminary vapour pressure deficit (VPD). The beans were kept well-watered throughout the exposure at the biomonitoring sites, therefore soil moisture was assumed not to be limiting stomatal conductance. Parameterisation of the bean stomatal conductance model is shown in Table 3.5, and the fits of the boundary lines to the individual stomatal conductance data points are shown in Figure 3.4.

To date, ozone fluxes have been calculated for the 2010 exposure period for Belgium-Tervuren, Spain-Valencia, Italy-Rome and Austria-Seibersdorf. Interestingly, for Belgium-Tervuren, Spain-

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Valencia and Italy-Rome, despite large differences in AOT40 calculated for each site, the POD0 and to a lesser extent the POD6 values for the sites were similar (Table 3.6). At the 24th ICP Vegetation Task Force meeting it was decided to scale down the ozone biomonitoring experiments and focus on collation of supporting evidence for ozone impacts on vegetation.

3.2.2

Ozone impacts on food security

Details on ozone impacts on food security are provided in Chapter 4.

3.2.3

Impacts of black carbon on vegetation

Background Black carbon (BC) exists as particles (aerosols) in the atmosphere and is a major component of soot. BC results from the incomplete combustion of fossil fuels, wood and other biomass. The black in BC refers to the fact that these particles absorb visible light. BC particles have a strong warming effect, contribute to global dimming, darken snow when deposited, and influence cloud formation (UNEPWMO, 2011). Hence, BC affects global and regional climate and has important regional impacts on temperature and precipitation, with particular impacts on the Arctic and other glaciated regions of the world. In the Himalayan region, heating from BC at high elevations may be just as important as CO2 in the melting of snow packs and glaciers (Ramathan and Carmichael, 2008). Other particles may have a cooling effect in the atmosphere and all particles influence cloud formation. There is a close relationship between emissions of BC (a warming agent) and organic carbon (OC; a cooling agent). They are always co-emitted, but in different proportions for different sources. The contribution to warming of 1 gram of BC seen over a period of 100 years has been estimated to be anything from 100 to 2,000 times higher than that of 1 gram of CO2 (UNEP-WMO, 2011). As the lifetime of BC in the atmosphere is short (days to weeks), any emission reductions will have immediate benefits. Here we provide a short overview on the impacts of BC on vegetation. Direct impacts of BC on vegetation Little is known about the direct impacts of BC on vegetation. Although several studies have investigated the impact of (road) dust on vegetation, we are only aware of one study that reported on the direct impact of BC: Hirano et al. (1995) showed that BC increased the leaf temperature by up to 3.7 oC due to additional absorption of incident radiation, with the level of increase depending on air temperature and light intensity. This increase in leaf temperature will be in addition to any rise in leaf temperature that might occur due to global warming (IPCC, 2007). How a plant will respond to such as increase in leaf temperature will depend on the species-specific temperature response of physiological processes such as stomatal conductance, photosynthesis, respiration and the resulting growth. An increase in leaf temperature might also results in an increase in transpiration, with consequence for the plant water balance and global water cycle. Enhanced transpiration is likely to aggravate the impacts of more frequent periods of drought in a future climate (IPCC, 2007). Direct impacts of (road) dust on vegetation More is known about the direct impacts of dust or more specifically road dust on vegetation. There have been numerous reports that dust of varying origin interferes with stomatal function, increases leaf temperature and transpiration, reduces photosynthesis and increases the uptake of gaseous pollutants (see Thomson et al., 1984; Farmer, 1993). Although Farmer (1993) reviewed the effects of dust on vegetation, most included studies reported on mineral dust originating from cement factories, gravel roads or limestone quarrying. In cucumber and kidney bean it was found that inert dust decreased stomatal conductance in the light, and increased it in the dark by plugging the stomata, when the stomata were open during dusting (Hirano et al., 1995). When dust of smaller particles was applied, the effect was greater. However, the effect was negligible when the stomata were closed during dusting. The dust decreased the photosynthetic rate by shading the leaf surface, with dust of smaller particles having a greater shading effect. Flückiger et al. (1977, 1978) observed a significant 13

decline in stomatal diffusive resistance in several tree species and shrubs exposed to road dust during hot hours in the afternoon and in the evening. As a consequence of particles blocking stomata, closure of stomata was inhibited. This caused an increase in transpiration, which had an antagonistic effect on the increase in leaf temperature (up to 6 oC) observed in illuminated leaves contaminated with dust. This might result in enhanced water stress and reduced growth during dry, hot periods. However, no effect on water content leaves (as indicator of turgor) was observed. Eller (1977) also reported an increase in leaf temperature by up to 4 oC in leaves of Rhododendron catawbiense contaminated with road dust. In Viburnum tinus, photosynthesis was reduced and this appeared to be due to shading when the upper surface of leaves was dusted and to impeded diffusion when the lower surface was dusted with black dust scraped from a car exhaust (Thomson et al., 1984). These effects were observed with 5 to 10 g dust per m2 leaf surface, whilst the maximum dust load found on the leaves of shrubs on the central reserves of motorways was about 2 g m-2. Therefore, the effects of dust on photosynthesis of Viburnum tinus grown near motorways is likely to be small. Trimbacher and Weis (1999) reported that the wax quality of needles of Norway spruce was poorer at polluted sites, possible related to the amount of dust present. It should be noted that the amount of dust deposited on the surfaces of leaves is species-specific, depending on the position of the leaf and smoothness and composition of the leaf surface. Indirect impacts of a mixture of air pollutants on vegetation Often, indirect impacts of a mixture of air pollutants (aerosols, atmospheric brown clouds - ABCs: the haze in the sky consisting of anthropogenic aerosols (BC, OC, SO4 and nitrates (NO3) among others) and pollutant gases such as CO and O3; see UNEP-WMO, in press) on vegetation have been studied or modelled via their direct impact on for example solar radiation reaching the earth surface and atmospheric temperature. Such studies make it difficult to distinguish impacts of BC from other atmospheric pollutants. Whilst there is confidence that BC and other aerosols affect cloudiness, precipitation and surface temperature, there are large uncertainties in the physical processes involved and the overall impacts are currently not well quantified (UNEP-WMO, in press). Field observations and semi-empirical (partially based on observations and partially on theory or models) studies (Ramanathan et al., 2001) have revealed that present-day BC induces large dimming (10–20 W/m2) at the surface over certain parts of the globe. This surface dimming, however, is smaller than the atmospheric solar absorption by BC, such that BC has a net positive radiative forcing and a net warming effect on the surface-atmosphere column. Comparing present day (2005) and pre-industrial concentrations of BC would imply an equilibrium global warming of 0.0 – 0.8 ºC, with regional variations occurring. For comparison, the equilibrium warming for the observed increase in CO2 over the same period is about 1.3 oC (UNEP-WMO, in press). There are strong regional variations in both concentrations and climate influences of BC and such variations can lead to substantial regional climate impacts. The warming effect of BC is greater in the northern hemisphere. For a review on the impact of global warming on vegetation and regional variations we refer to the recent IPCC reports (2007) and Vandermeiren et al. (2009). Because BC absorbs light, it not only decreases the amount of solar radiation reaching the surface but also changes the direct-to-diffuse radiation ratio. The latter depends on concentrations of BC (nonscattering aerosols), their source (fossil fuel or biomass burning) (Ramana et al., 2010), and the concentration of scattering aerosols (e.g. SO4) (Liepert and Tegen, 2002, Ramana et al., 2010). Increasing amounts of scattering aerosols enhance the diffuse component of the radiation reaching the surface, whereas increasing concentrations of absorbing aerosols such as BC have the opposite effect. There is observational evidence that plants are overall more efficient under diffuse radiation conditions (Gu et al., 2002; Niyogi et al., 2004; Knohl and Baldocci, 2008; see also Roderick et al., 2001). Aerosol-induced increases in diffuse radiation after volcanic eruptions can enhance the terrestrial carbon sink by stimulating photosynthesis via a reduction of the volume of shade within canopies. This can contribute to a temporary decline in the growth rate of atmospheric carbon dioxide concentrations and global warming (Gu et al., 2003; Roderick et al., 2001) Only recently have global models been able to account for effects of aerosols on vegetation. This is done by accounting separately for direct and diffuse radiation and by dividing photosynthesis between

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sunlit and shaded leaves. A first attempt to quantify the effects of all types of aerosols (scattering and absorbing) and clouds on the regional and global carbon sinks has estimated changes in the diffuse fraction of -5 to 30% during the global dimming period (1950-1980) which correspond to a contribution to the regional carbon sink of up to 30 g C/m2/yr- across Europe, the eastern USA, East Asia and some tropical regions in Asia (Mercado et al., 2009). Conversely, during the brightening period (19802000), a reduction in the diffuse fraction over Europe, eastern USA, western Australia, and some regions of Russia and China, led to a lower regional contribution to the land C sink from diffuse radiation. Globally, over the 1960-2000 period, diffuse radiation effects associated with changes in aerosols and clouds in the atmosphere enhanced the land C sink by about 25%. This more than offsets the negative effect of reduced surface radiation on the land C sink, giving a net effect of changes in radiation on the land carbon sink of 10% (Mercado et al., 2009). Hence, aerosols contribute an additional climate cooling by increasing the efficiency of photosynthesis, thus removing CO2 from the atmosphere. However, under a climate mitigation scenario for the twenty-first century in which sulphate aerosols decline before atmospheric CO2 is stabilized, this diffuse-radiation fertilization effect declines rapidly to near zero by the end of the twenty-first century. The framework used by Mercado et al. (2009) could be used to evaluate the impacts of BC alone on land C uptake through the combination of reductions on surface radiation and concomitant changes in temperature and atmospheric vapour pressure deficits. Mitigation of emissions of BC Efforts to mitigate BC will reduce concentrations of BC as well as OC. The warming effect of BC and the compensating cooling effect of OC introduce large uncertainty in the net effect of any BC mitigation of global warming. This uncertainty is particularly large for mitigation options that focus on biomass cooking stoves and open biomass burning and much smaller for those that focus on fossil fuels (i.e. diesel) because biomass combustion emits significantly more OC compared with fossil fuel burning. A full understanding of the impact of aerosols and BC on climate and the global carbon cycle requires consideration of the biophysical responses of terrestrial vegetation as well as atmospheric radiative and thermodynamic effects (Steiner and Chameides, 2005). Globally, the surface cooling effect of ABCs may have masked as much 47% of the global warming by greenhouse gases, with an uncertainty range of 20–80%. This presents a dilemma since efforts to curb air pollution may unmask the ABC cooling effect and enhance the surface warming. Thus efforts to reduce GHGs and air pollution should be done under one common framework (Ramathan and Feng, 2009).

3.2.4

Progress with European heavy metals and nitrogen in mosses survey 2010/11

The European moss biomonitoring network was originally established in 1990 to estimate atmospheric heavy metal deposition at the European scale. The moss technique is based on the fact that carpetforming, ectohydric mosses obtain most trace elements and nutrients directly from precipitation and dry deposition with little uptake from the substrate. The technique provides an alternative, timeintegrated measure of heavy metal and potentially nitrogen deposition from the atmosphere to terrestrial ecosystems (Harmens et al., 2010; in press). It is easier and cheaper than conventional precipitation analysis as it avoids the need for deploying large numbers of precipitation collectors with an associated long-term programme of routine sample collection and analysis. Therefore, a much higher sampling density can be achieved than with conventional precipitation analysis. In 2008, the ICP Vegetation Task Force agreed to conduct the next European survey on heavy metal and nitrogen concentrations in naturally occurring mosses in 2010/11. Between 24 – 27 countries will submit data on heavy metals, of which 14 countries will also submit data on nitrogen concentrations in mosses (Table 3.7). The Programme Coordination Centre has received already data from three countries. In 2010, the Task Force recommended to include a pilot study on mosses as biomonitors of persistent organic pollutants (POPs) and six countries have agreed to submit data on POPs (Table 3.7). In contrast to heavy metals, the use of mosses for monitoring atmospheric deposition of organic compounds such as polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) has so far received little attention (Holoubek et al., 2000; Zechmeister et al., 2003). This is surprising

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as mosses have been shown for example to retain atmospherically deposited PAHs as efficiently as trace metals (Milukaite, 1998). A review on the use of mosses as biomonitors of POPs is provided in the next section. In addition, some countries will also determine the sulphur concentration in mosses. Table 3.7. Countries (regions) participating in the European moss survey 2010/11. All countries will determine heavy metals; countries in bold will also determine nitrogen. POPs: countries that participate in the pilot study for POPs. Albania Austria Belarus Belgium Bulgaria Croatia Czech Republic Denmark (Faroe Islands) Estonia

Background Persistent organic pollutants (POPs) are organic substances that: (i) possess toxic characteristics; (ii) are persistent; (iii) bioaccumulate; (iv) are prone to long-range transboundary atmospheric transport and deposition; and (v) are likely to cause significant adverse human health or environmental effects near to and distant from their source (LRTAP Convention, 1998). They are mainly of anthropogenic origin, show weak degradability and consequently are accumulating in the environment across the globe, including remote areas such as the (Ant)Arctica. The combination of resistance to metabolism and lipophilicity (‘fat-loving’) means that POPs will accumulate in foodchains (Jones and de Voogt, 1999). The 1998 Aarhus Protocol on POPs of the LRTAP Convention and the 2001 Stockholm Convention on POPs, a global treaty under the United Nations Environment Programme (UNEP), aim to eliminate and/or restrict the production and use of selected POPs. The main persistent organic pollutants (POPs) are polychlorinated biphenyls (PCBs), dioxins (polychlorinated dibenzo-p-dioxins; PCDDs), furans (polychlorinated dibenzofurans; PCDFs), hexachlorobenzene (HCB), organochlorine pesticides (OCPs; e.g. DDT, aldrin), polycyclic phenols and polycyclic aromatic hydrocarbons (PAHs) (Jones and de Voogt, 1999). The majority of these compounds are toxic for human beings and some are classified carcinogenic, mutagenic and/or teratogenic (i.e. reprotoxic; Belpomme et al., 2007). Their ecotoxicity was also highlighted in aquatic (Leipe et al., 2005) and terrestrial ecosystems (Oguntimehin et al., 2008; Smith et al., 2007). In Europe the emission and deposition of POPs are monitored and modelled by the European Monitoring and Evaluation Programme (EMEP; Shatalov et al., 2010). The impacts of POPs on the environment and human health are studied by the Working Group on Effects of the LRTAP Convention. In the currently ongoing European moss survey of 2010/11 some countries will determine the concentration of selected POPs (PAHs in particular) in mosses to investigate the suitability of mosses as biomonitors of POPs at a regional scale (see section 3.2.4). As mosses do not have a root system or cuticle, they adsorb/absorb nutrients and pollutants from the air, which often accumulate on or in moss tissue. The accumulation is aided by the high surface to volume ratio of moss tissue. The monitoring of heavy metal and nitrogen concentrations in naturally growing mosses allows determination of spatial patterns and temporal trends of heavy metal and nitrogen pollution and deposition at a high spatial resolution (Harmens et al., 2010, in press). Although mosses have also been used to monitor POPs pollution, the number of studies is limited and most studies have focussed on PAHs. Here we review the application of mosses as monitors of POPs pollution.

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PAHs pollution and biomonitoring with mosses PAHs are a family of chemical compounds constituted by carbon and hydrogen atoms which form at least two condensed aromatic rings. The majority of PAHs originate from fossil or non-fossil fuels by pyrolysis or pyrosynthesis. PAHs are emitted in the atmosphere mainly from anthropogenic source but they also originate from natural sources such as volcanic eruptions and forest fires (Simonich and Hites, 1995). The main sources of PAHs in the environment are aluminium production, coke production from coal, wood preservation and fossil fuel combustion (traffic, domestic heating, electricity production; Wegener et al., 1992). Eight PAHs have been classified by US Environmental Protection Agency as potentially carcinogenic (US EPA, 1997). The mechanism of uptake of organic pollutants by vegetation is governed by the chemical and physical properties of the pollutant (such as their molecular weight, aqueous solubility, and vapour pressure), environmental conditions (atmospheric temperature), and the plant species and structure (Simonich and Hites, 1995). After emission in the atmosphere, the most volatile PAHs remain in gaseous phase whereas the least volatile (5 or 6 rings) are adsorbed on solid atmospheric particles. Deposition to vegetation occurs through uptake of the lipophilic compounds in both vapour and particle phases, but there may also be a removal at higher ambient temperatures or when the concentration in the air decreases. PAHs of intermediate volatility (3 or 4 rings) are distributed between gaseous and particulate phases (Viskari et al., 1997). In the winter, however, PAHs are predominantly in the particulate phase due to increased emissions and their low degree of volatilization at low temperatures. PAHs in the gaseous phase are generally transported to areas remote from main pollution sources, whereas particulate absorbed PAHs are generally deposited in higher proportions near emission sources (Thomas, 1986). This might explain why often PAHs in mosses sampled away from local pollution sources are dominated by smaller ring numbers of 3 or 4 (Dołęgowska and Migaszewski, in press; Gałuszka, 2007; Migaszewski et al., 2009; Orliński, 2002; see table 3.8). Gerdol et al. (2002) observed that the fraction of low molecular weight volatile PAHs was greater in rural compared to urban sites. On the other hand, the dominance of 3 ring compounds appears to be related to the type of pollution source as are the dominance of individual PAHs (Foan et al., 2010). Phenanthrene, fluoranthene and pyrene have often been reported as the dominant PAHs in mosses sampled away from pollution sources (Foan et al, 2010; Gałuszka, 2007; Krommer et al., 2007; Zechmeister et al., 2006; see table 3.8). In Hungary, a good correlation between total PAHs concentrations in Hypnum cupressiforme and traffic volume was observed, but not with population density, with 99% of the total PAHs concentration in the moss consisting of low molecular weight (Ötvös et al., 2004). Most studies so far have determined the concentration of POPs in mosses as an indication of pollution levels, in particular in remote areas. Few studies have related the concentration in mosses with total atmospheric concentrations or deposition rates. Thomas (1984, 1986) found linear relationships between the accumulation of selected PAHs in Hypnum cupressiforme sampled from tree trunks and their concentration in rain water and atmospheric particulate matter, taking into account also the amount of precipitation. The concentration in mosses in the autumn represented mean atmospheric pollution levels in the previous year. He concluded that mosses are most appropriate for measuring environmental chemicals which are deposited in particulate form on the mosses and can be physically retained by them. Milukaite (1998) found that the flux of benzo(a)pyrene from the atmosphere to the ground surface correlated well with its concentration in mosses. However, it should be noted that the accumulation of trace substances in mosses is not only dependent on atmospheric pollution levels but also on enrichment parameters which describe physiological parameters as well as pollutant characteristics (Thomas, 1984). In addition, the presence of water from precipitation might be necessary for PAH accumulation in mosses. Thomas (1986) reported on a marked gradient of the concentration of selected PAHs in mosses in western-northern Europe in agreement with the presence of pollution sources.